(1)Field of the Invention
The present invention relates to line photosensor and particularly line photosensors in which a plurality of sensor elements are disposed in a row or rows on the same substrate and the respective output leads from the sensor elements are wired in an electrically isolated and laminated manner.
(2)Related Background Art
With the recent advancement of image processing techniques, facsimile devices have generally spread rapidly. Also, digital reproduction devices and input image readers for personal computers have been developed. In such a device, to be able to input an image as digital quantities requires an image sensor, a so-called line photosensor, which reads an image by scanning the same electrically in one direction and mechanically in the transverse direction. The most prevailing line photosensor is of a CCD type. In order to miniaturize the entire device, the development of a contact type reading sensor has been expedited, including a short-optical path self-focusing fiber array (Nihon Sheet Glass "SELFOC" (trade name)) having a length equal to at least the width of a document to be read. The reading sensor normally has no self-scan function to output image information externally from the respective sensor elements and requires the provision of an additional scan circuit therefor. In this case, output leads are needed for the respective sensor elements between these elements and the scan circuit. When an increase in the number of sensor elements is required as in the case of high-precision reading or color reading, the respective leads should be very thin and occurrence of lead disconnections and/or shortcircuits between adjoining leads cannot be prevented. In order to solve this problem, for example, a line photosensor having a laminated structure as shown in FIG. 1 has been proposed in the past. FIG. 1(a) is a plan view of the photosensor and FIG. 1(b) is a cross-sectional view taken along the line A-A of FIG. 1(a).
Reference numeral 1 denotes a glass substrate on which a photoconductor 2, for example, of amorphous silicon, is formed. Attached to photoconductor 2 are a common electrode 3 and individual electrodes 4 and 5, to form two coplanar sensor elements. Different-color filters 6 and 7 are disposed between the respective sensor elements and the substrate, and the respective sensor elements are formed so as to be sensitive to different colors. An insulating layer 38 is provided between the extract wiring electrodes 8 and 9. Electrodes 8 and 9 are connected by junction leads 43 and 44 to corresponding drive ICs 13 and 14, respectively. This arrangement has an advantage that it can prevent the extract wiring electrodes 8 and 9 from being excessively thin and facilitate wiring between the ICs and the respective sensor elements. If there is a voltage difference between the extract wiring electrodes 8 and 9, however, the two corresponding sensor element outputs will effect each other.
On the other hand, if a method of storing the photocurrent from each sensor element for a fixed duration is employed as the method of driving the sensor element, and particularly if the sensor is a photoconductive type line photosensor which allows a large current to flow therethrough, a photocurrent storage capacitor is needed for each sensor element. In this case, as shown in FIG. 2, the extract wiring electrodes 9 and 10 are provided at the corresponding ends of substrate 1, grounding electrodes 41 and 42 are provided by the medium of insulating layers 39 and 40 under the electrodes 9 and 10, respectively, so that each set of electrode 9, insulating layer 39 and grounding electrode 41 constitutes one capacitor while a corresponding set of the electrode 10, insulating layer 40 and grounding electrode 42 constitutes the other capacitor. Since this type of line photosensor has the extract wiring electrodes 9 and 10 at the corresponding ends of the substrate, the desired degree of miniaturization cannot be attained. Also, each of the extract electrodes 9 and 10 is used as one electrode of the corresponding capacitor. Thus if the length of each electrode is shortened to miniaturize the entire line sensor, the electrode areas, and hence capacity of a capacitor, will be reduced.